Direct operated cartridge valve assembly

1. A cartridge valve assembly comprising: a body having a central bore, a first port, a second port, and a third port fluidly connected to the central bore; a main spool having a first end and a second end positioned within the central bore between a first stop member and a second stop member, the main spool movable between at least a first position and a second position, wherein the main spool forms, within the central bore, a first chamber between the first end and the first stop member, a second chamber between the second end and the second stop member, and a control chamber between the first and second ends; a balance spring positioned in the first chamber and adapted to apply a force at the first end of the main spool; a first passage fluidly coupling the first chamber to the second chamber; an actuator adapted to apply a force to the first end of the main spool; a feedback spool positioned in the second chamber, the feedback spool having a distal end section slidably positioned in a central bore of the second stop member to form a feedback chamber; a feedback spring positioned in the second chamber around a section of the feedback spool and the second stop member, and adapted to apply a force at the second end of the main spool and urge the main spool from the second position to the first position; and a second passage fluidly communicating the control chamber with the feedback chamber.

2. The cartridge valve assembly of claim 1 , wherein the balance spring is positioned around a section of the main spool and adapted to urge the main spool from the first position to the second position.

3. The cartridge valve assembly of claim 1 , wherein the first passage is defined within the main spool.

4. The cartridge valve assembly of claim 1 , wherein the second passage is positioned outside of the body.

5. The cartridge valve assembly of claim 1 , wherein the feedback chamber is at least partly defined by an end surface of the distal end section of the feedback spool and inner walls of the central bore of the second stop member.

6. The cartridge valve assembly of claim 1 , wherein the main spool includes a first end section, a second end section and an intermediate section, wherein the intermediate section has a smaller diameter than the first end section and the second end section, and the intermediate section and the central bore of the body form the control chamber.

7. The cartridge valve assembly of claim 6 , wherein the surface area of the first end section of the main spool adapted to be in contact with fluid in the control chamber is smaller than the surface area of the second end section of the main spool adapted to be in contact with fluid in the control chamber.

8. The cartridge valve assembly of claim 1 , further including a housing forming a cavity, and including a first port, a second port, and a third port fluidly connected to the cavity, wherein the body is received in the cavity, and the first port, the second port, and the third port of the body are respectively in fluid communication with the first port, the second port, and the third port of the housing.

9. The cartridge valve assembly of claim 1 , wherein the actuator is a solenoid actuator including an armature coupled to the first end of the main spool to apply the force to the first end of the main spool.

10. A method of operating a cartridge valve assembly, the method comprising: applying a force to a first end of a main spool of the cartridge valve assembly using a balance spring positioned in a first chamber around a first section of the main spool to move the main spool from a first position to a second position, the main spool being slidably positioned within a body of the cartridge valve assembly between a first stop member at the first end and a second stop member at an opposite second end to define the first chamber at the first end, a second chamber at the second end, and a control chamber between the first and second ends, the first position being a position in which a tank port of the body is fluidly coupled to a fluid actuator port of the body through the control chamber, and the second position being a position in which the tank port is fluidly decoupled from the fluid actuator port and a pump port of the body is fluidly coupled to the fluid actuator port through the control chamber, the tank port being at least partially exposed to the first chamber in the second position; directing fluid from the control chamber to a feedback chamber situated within the second stop member, wherein the fluid in the feedback chamber applies a feedback pressure to a surface of a feedback spool slidably positioned in the feedback chamber, the feedback pressure being substantially equal to the fluid pressure in the control chamber, and wherein the feedback spool applying a force to the main spool to move the main spool from the second position toward the first position; and applying a force at the second end of the main spool using a feedback spring positioned in the second chamber to move the main spool from the second position to the first position to fluidly decouple the pump port from the fluid actuator port and fluidly couple the tank port to the fluid actuator port through the control chamber.

11. The method of claim 10 , further including connecting the first chamber to the second chamber to balance the pressure at the first end of the main spool and the second end of the main spool.

12. A hydraulic actuation system comprising: a housing forming a cavity, and including a first port, a second port, and a third port fluidly connected to the cavity; a first pressure source fluidly connected to the first port of the housing; a fluid actuator fluidly connected to the second port of the housing; a second pressure source fluidly connected to the third port of the housing, wherein the second pressure source has a relatively higher pressure than the first pressure source; and a cartridge valve assembly including: a body adapted to be inserted into the cavity of the housing, and including a central bore extending along a central axis, a first port, a second port, and a third port fluidly connected to the central bore, wherein the first port, the second port, and the third port of the body are respectively in fluid communication with the first port, the second port, and the third port of the housing; a main spool positioned within the central bore and being movable between at least a first position and a second position, wherein the main spool forms, within the central bore, a first chamber at a first end of the main spool, a second chamber at an opposite second end of the main spool, and a control chamber between the first and second ends, an actuator adapted to apply a force to the first end of the main spool; a balance spring positioned in the first chamber around a first end section of the main spool and adapted to apply a force at the first end of the main spool; a feedback spool positioned in the second chamber having an end surface exposed to a feedback chamber that is fluidly coupled to the control chamber, the feedback spool being adapted to apply a force to the second end of the main spool; a feedback spring positioned in the second chamber and adapted to apply a force at the second end of the main spool; and a first passage fluidly communicating the first chamber with the second chamber.

13. The hydraulic actuation system of claim 12 , wherein the feedback spring is adapted to urge the main spool from the second position to the first position.

14. The hydraulic actuation system of claim 12 , wherein the actuator adapted to apply a force to the first end of the main spool is a solenoid actuator including an armature coupled to the first end of the main spool to apply the force to the first end of the main spool.

15. The hydraulic actuation system of claim 12 , wherein the body includes a stop member at the second end of the body including a central bore therein, and wherein the feedback chamber is formed within the central bore of the stop member.

16. The cartridge valve assembly of claim 12 , wherein the first passage is defined within the main spool.

17. The hydraulic actuation system of claim 12 , wherein the second passage is positioned outside of the body.